Effect of chromium and carbon contents on the sintering of WC-Fe-Ni-Co-Cr multicomponent alloys

Abstract

WC-Fe-Ni-Co-Cr cemented carbides have been obtained by liquid phase sintering from WC-Fe-Ni-Co-Cr3C2 powder mixtures. Taking the 40wt%Fe-40wt%Ni-20wt.%Co alloy as a reference, new binder phases has been prepared by introducing controlled amounts of Cr and C, via Cr3C2 and C black powders respectively. As described for WC-Co-Cr materials, Cr additions are observed to reduce the eutectic temperatures of the WC-Fe-Ni-Co system. First liquids detected on heating exhibit wide temperature melting ranges, which become narrower and are displaced to higher temperatures on repeated heating and cooling cycles. Apart from the decarburization associated to the carbothermal reduction of powder oxides, this phenomenon could be also associated to the homogeneization of the chemical composition of these multicomponent binder phases, which is faster as C content decreases. Correlation between experimental melting and solidification temperature ranges and those predicted by Thermocalc (R) is better as Cr content increases. Experimental C windows, defined in this work by the absence of free C or. phases, are located at C contents higher than those estimated by Thermocalc (R). Although the 40wt.%Fe-40wt.%Ni-20wt.%Co alloy is austenitc, BCC phases are partially stabilized at low C and high Cr contents. Although these compositions are free from. phases or free C, a precipitation of Cr-rich carbides is found at the WC-metal interface. These precipitates are not observed in the alloy with 0.75 wt% Cr (i.e. 5 wt% of the nominal metal content) and 5.39 wt%C. This C content is 0.17 wt% higher than that predicted for precipitation of M7C3.